Research On Formation Conditions And Danger Degree Of Debris Flow In The Tianchi Lake Area Of Changbai Mountains

Changbai Mountains is located in the frontier between the DPRK and the southeast part of Jilin Province, China, with a width of 200km in the east-west direction and a length of 310km in the south-north direction. It is a very famous natural protection area and scenic tourist resort. The Tianchi Lake area of Changbai Mountains is famous in the world because it has a unique volcano land form, intact ecocystem, beautiful natural landscape, which makes it natural science explore and tourist sight-seeing attraction.However, debris flow disasters are concentrated in the Tianchi Lake area of Changbai Mountains and happen frequently because of its special volcanic geoenvironmental background. About 20km2 range in the north of Changbai Mountains waterfall, in the two sides of mountains located in Erdaobai river source region, there are more than ten gullies where debris flows break out, of which, Heifengkou and Tianshang hot spring debris flows often break out, be worth of emphasizing recognition. The debris flow disaster not only destroys the precious biological resources seriously but also hampers the development of local tourist industry. In order to understand deeply the development and formation rules, offer the suggest for the prevention and protection of debris flows and alleviate the influence of debris flow disaster on the natural environment and human activities, the paper puts emphasis on the formation conditions, types, distribution and granularity features of accumulation of debris flows. 8 gullies are chosen to evaluate their danger degree, disaster and prevention focus.As we all know that debris flow is the result of the geological and meteorological conditions combining with each other, it is formed under three fundamental conditions, that is, plenty of loose fragmental materials, steep topography and rapid and heavy downpour. The special geoenvironmental background and natural condition make debris flow develop in Tianchi Lake area of Changbai Mountains. 1) The stratigraphical lithology and tectonical conditions contribute to the formation of loose fragmental materials. The main body of the outcropping rock layer is composed of deep gray trachyte of Baitoushan formation of mid-Pleistocene series and yellow, brown yellow volcanic-tuff crust of weather. This kind of structure that weak layers and hard layers emerge alternately contributes to the instability of rock mass. Furthermore, large-scale fold and fault structure hasn't been found around the Tianchi Lake, but the original prismatic joints and radial joints developed well in the trachyte, so the rock mass is dissected into fractured fragmental structure and the integration of rock mass is further destroyed. It is the combined action of inner and external geological forces that make the collapsed and slumping accumulation in the slope distribute widely and offer plenty of loose fragmental materials for the debris flow. 2)The landform of two sides of Erdaobai River to the north of Changbai Mountains waterfall is high and steep. The relative elevation is above 300m and the gully on the hill lope developes well. All these create the favorable conditions for the debris flows. 3)The meteorological condition in the area helps to form debris flow. On the one hand,freezing-melting action in this area is very violent. In winter, the freezing of water filled in the joints and fissures in rock mass,will create expansion force within the rock mass. In summer,when ice and snow melt, water pressure, softening and mudding make strengthen of rock mass decrease. On the other hand, big temperature difference results in unevenly affected heated. The weathering and collapsing process of surface rock mass is accelerated. The climate feature helps the formation of loose solid material. The concentrated and plentiful rainfall in the area not only offers liquid material for the debris flow, but also offers the dynamical condition for the accumulation of fragmental materials. Rapid rainfall is stimulus factor of debris flow too. In a word, all kinds of special...